Miniature thermoelectric cooler

ABSTRACT

A miniature thermoelectric cooling device for storing small amounts of thermally unstable substances, like drug vials with insulin for diabetic patients or protein based drugs for thrombolytic therapy, is disclosed. A solar energy collector coupled with a rechargeable battery is provided as the energy source. The miniature cooler is small enough to be belt-carried at all time by a person, whose life or health depends on the drugs. When switched to a heating mode, the thermoelectric device can temporarily elevate the temperature of the drug to a body temperature thus providing comfortable conditions for the injection. A combined solar-and-battery power supply allows keeping an article in the cooler at low temperatures around o&#39;clock at all times during substantially long travels in hot or tropical conditions where even short term exposure to surrounding temperatures can destroy the potency of the drug.

FIELD OF INVENTION

[0001] This invention relates to thermoelectric temperature controldevices, used for creating a zone of lowered temperatures for storingarticles with low thermal stability. The invention is most suitable forstoring small articles, mainly drug vials with protein based drugs,primarily insulin for the diabetic patients or drugs for out-of-hospitalthrombolytic therapy.

DESCRIPTION OF THE PRIOR ART

[0002] Portable coolers that can be comfortably carried by a person arewell known. Typically, such coolers comprise a storage compartment withthick walls, fabricated of a polystyrene foam with closed cells andprovided with a lid and a carrying handle. For a limited time thisthermally isolated compartment can maintain constant temperature. Tocompensate for the heat transfer that does occur through the walls ofthe compartment and to maintain a low temperature in the compartment forlonger period of time, a thermoelectric, or Peltier, device is oftenemployed.

[0003] According to the Peltier effect, an electric current passingthrough the junction of two dissimilar materials causes generation orabsorption of heat, with the direction of heat flow depending upon thedirection of the current. The rate of the thermal effect—the heatflow—is proportional to the magnitude of the current. By positioning amultitude of such junctions thermally parallel and electrically inseries in a small space a significant thermal effect can be achieved.Such devices are now commercially available with junctions of n-type andp-type semiconductors materials. These devices are operable in a rangeof DC voltages. A fan, generally associated with the device, is used tocirculate air from the p-n junctions to the region where the thermaleffect is desirable.

[0004] About 16 million of people in the United States and 120 millionpeople worldwide suffer from diabetes. Life and health of a significantnumber of these patients often depends on daily injections of insulin.Insulin, like many other protein based drugs, has relatively low thermalstability. The storage of insulin solution in vials requires lowtemperature environment, preferably a temperature range 4-10 degreesCentigrade. At room temperature an insulin solution can preserve itspotency only for a limited period of time, at most several weeks. Whentraveling, people with diabetes experience additional inconvenienceassociated with lack of low temperature environment required for thestorage of insulin. In a tropical climate or during a hot day at thebeach even short term exposure of the insulin to elevated temperaturescan destroy its potency and thus jeopardize the health or even life of adiabetes patient. This is especially true for long vacations duringsummer time in the United States or in other countries with hot climate.

[0005] In U.S. Pat. No. 5,379,594 a portable, hand-held, solar energythermoelectric device for the use, storage and transportation ofsubstances requiring a temperature controlled environment in a wideambient temperature range is disclosed. The storage chest described inthe patent has at least 1 cubic foot of usable volume and consumes about70 watts of electric power from generated by a solar energy collector.This thermoelectric chest is too large to meet the requirements for adrug storing cooler capable of being carried at all the time with aperson.

[0006] In U.S. Pat. No. 4,981,019 a portable food container isdisclosed. It is cooled by a solar powered refrigeration unit andincludes a thermoelectric power unit and heat pipes so that thecontainer will be cooled even when there is no solar radiation and willhave an even temperature distribution. The intended use of the cooler isa picnic food container. Once again, this device is too large to beconveniently carried by a person at all times.

[0007] It is desirable to develop a miniature temperature controlleddevice, which could be carried with a person at all time and wouldguarantee stability of the insulin or other drug during several monthsin hot or tropical climate.

[0008] It is an object of the present invention to provide a miniaturethermoelectric cooler that can be carried with a person at all time.

[0009] It is another object of the present invention to provide a coolerwith a power supply comprising a solar energy collector coupled with anelectrical rechargeable battery, with an overall capacity of largeenough to power the cooler around the clock during days and nights atall times.

SUMMARY OF THE INVENTION

[0010] The present invention is a miniature belt-carried cooler intendedfor long term storage of small articles, particularly drugs, at loweredtemperatures. The present invention comprises a thermally isolatedstorage compartment, a solar power collector coupled with a rechargeableelectric battery and a thermoelectric unit. The solar energy collectorand rechargeable batteries are secured to the side walls of the storagecompartment and serve as a power supply for the thermoelectric systemproviding control of the temperature inside the storage compartment. Thethermoelectric system includes a block of Peltier elements, aprogrammable control unit, mounted on the top wall of the storagecompartment, and a temperature sensor placed inside the storagecompartment.

[0011] The storage compartment is made of thermally insulatingmaterials, with its top wall openably connected to the side wall of thecompartment. The storage compartment may include a Dewar flask foradditional thermal insulation of the stored article.

[0012] A solar energy collector generates enough power to cool thecompartment and to recharge the battery at the same time. Thecapacitance of the fully charged electric battery is sufficient to powerthe thermoelectric system during nights, when solar energy is notavailable.

[0013] The hot end of the Peltier unit extends up from the top wall ofthe storage compartment, whereas the cold end of the unit extends downfrom the top wall inside the storage compartment. The hot end of thePeltier unit is provided with a radiator, which serves as a heat sink,dissipating heat to the surrounding air.

[0014] A belt for wearing a cooler in accord with the present inventionat a person's waist may be provided.

[0015] The foregoing objects of the invention will become apparent tothose skilled in the art when the following detailed description of theinvention is read in conjunction with the accompanying drawings andclaims. Throughout the drawings, like numerals refer to similar oridentical parts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a perspective view of a miniature thermoelectric coolerin accord with the present invention.

[0017]FIG. 2 is a schematic view of the miniature thermoelectric coolershown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention comprising a miniature thermoelectriccooler 10 will be described with reference to FIGS. 1 and 2. Cooler 10comprises a thermally insulated compartment 12 adapted for storage ofthe drug vials or other small articles 14 at lowered temperatures. Thecompartment 12 has a bottom wall 16 and side walls 18 made of athermally insulating material, such as a closed cell foam material. Atop wall or lid 20 of the compartment is openably-connected to its sidewall 18. Compartment 12 may include a Dewar or double wall flask 22,made of glass or stainless steel.

[0019] A thermoelectric unit 24 is shown attached to the lid 20. A heatsink 26 is attached to the hot or upper end 28 of the thermoelectricunit 24. Heat sink or radiator 26 protrudes through an appropriatelyconfigured opening 30 in the top wall 12 so as to be exposed to theambient environment. That is, the heat 26 sink serves for cooling of thehot end 28 of the thermoelectric device by the surrounding air.

[0020] Preferably, the cooler 10 is powered by a renewable energyresource. By way of example, cooler 10 may include a photovoltaiccollector panel 32 for collecting the solar energy during day timehours. Panel 32 will provide electric power to charge one or moreelectric batteries 34, which provide power to the thermoelectric coolingsystem during nights, when the solar energy is unavailable.Advantageously, the power output of the solar battery 34 may be lessthan 10 watts. A programmable control unit 36 may be mounted on the topwall 20 to provide control of the temperature inside the storagecompartment 12. The temperature inside the storage compartment may bemeasured by a temperature sensor 38. The whole cooler assembly issecured on a waist belt 40, which allows to comfortably carry the coolerat all time.

[0021]FIG. 2 schematically shows a cross section and electric circuitsof a cooler in accord with the present invention. The miniature coolermay comprises a compartment 12 having a volume of 100-250 cubiccentimeters with the top wall 20 and side walls 18 fabricated of aclosed cell polymeric foam, such as polystyrene. Located interior to theside walls 18 is the Dewar flask 22. The flask 22 includes a space 42between the two walls 44 and 46 thereof, which is evacuated to a highlevel of vacuum. The vacuum between the walls 44 and 46 reduces thetransfer of heat to or from the cooler 10. Dewar flasks provideexcellent thermal insulation from environment and often are used forstoring liquid gases.

[0022] As noted, a thermoelectric unit 24 is secured in the middle ofthe top wall 12 with its cold end 48 facing the interior of the Dewarflask 22 and the hot end 28 attached to the heat sink 26. Thethermoelectric unit 24 consists of two or more elements 50 ofsemiconductor material (such as bismuth telluride) that are connectedelectrically in series and thermally in parallel. These thermoelectricelements 50 and their electrical interconnects are mounted between twoceramic substrates 52 and 54 at their top and bottom ends 28 and 48respectively. The substrates 52 and 54 serve to hold the overallstructure together mechanically and to insulate the individual elements50 electrically from one another and from external mounting surfaces.Preferably, the various components of the cooling elements 50 areintegrated in a cylindrical plug (not shown for purposes of clarity)that fills the neck of the Dewar flask 22. During operation of thecooler the semiconductor elements 50 actually are moving the heat fromthe colder end of the compartment 12 to the upper hotter end 28 and heatsink 26. The thermoelectric unit 24 is powered by a low voltage directcurrent from rechargeable batteries 32 located outside the storagecompartment. A thermocouple 38 or other temperature sensor, placedinside the storage compartment, measures the temperature to which storedarticles 14 are exposed.

[0023] A signal from the thermocouple 38 comes to the controller 36 andis used for stabilization of the temperature inside the storagecompartment at a preprogrammed level. The controller 36 turns on and offthe thermoelectric unit 24 depending on the temperature inside thecompartment. During the “off” state, the heat exchange between theinside volume of the container and the environment outside is minimal.In part this is due the fact that the thermal convection inside thecontainer 12 is very low, because the articles 14 at the bottom of thecontainer 12 are colder than the ceramic substrate 54 above them. Whenthe thermoelectric unit 24 is on, the plate 54 becomes colder then thebottom of the compartment and convection heat flow starts pumping heatfrom the bottom to the flask to the cold end 48 of the thermoelectricunit 24. The overall device thus is very efficient in keeping theinternal part of the Dewar flask cold, with very low energy being spent.The operational state of the cooler is vertical with the heat sink andthe hot end of the thermoelectric unit positioned above the storagecompartment.

[0024] The present invention having thus been described, othermodifications, alterations, or substitutions may now suggest themselvesto those skilled in the art, all of which are within the spirit andscope of the present invention. For example a miniature cooler in accordwith the present invention may include a universal electrical adapterwhich allows the operator to use power from electric current sources ofother direct current voltages or 120 and 220 volts alternating current.In addition, the present invention could further include a heating modeof operation of the thermoelectric unit 24 during which the temperatureof the insulin or another drug can be elevated to the body level thusmaking injections more comfortable for the patient. It is thereforeintended that the present invention be limited only by the scope of theattached claims below.

What is claimed is:
 1. A miniature cooler comprising: a storagecompartment made of thermally insulating materials and having top andside walls with said top wall openably-connected to said side wall suchthat said top wall closes the compartment or allows access to thecompartment; a power supply including a photovoltaic collector panel anda rechargeable battery, said panel being externally attached to saidcompartment sidewall and electrically connected to said rechargeablebattery, said photovoltaic collector being provided for generating tocool said compartment and to recharge said battery; and a temperaturecontrol system comprising: a thermoelectric unit imbedded in said topwall of the compartment, said unit having a hot end and a bottom end,said hot end of said unit facing upwardly and said cold end of said unitfacing downwardly from said top wall, respectively; a control unitoperationally connected to the thermoelectric unit and the power supply,said control unit being provided for selectively turning saidthermoelectric unit on and off; and a temperature sensor placed insidethe storage compartment and operatively connected to said control unit.2. The miniature cooler of claim 1 wherein: the storage compartmentfurther additionally includes a Dewar flask, in which the articles to bestored are placed.
 3. The miniature cooler of claim 1 wherein: thevolume of the storage compartment is less than 250 cc.
 4. The miniaturecooler of claim 1 wherein: the power output of the solar battery is lessthan 10 W.
 5. The miniature cooler of claim 1 wherein saidthermoelectric unit comprises semiconductors connected electrically inseries and thermally in parallel.
 6. The miniature cooler of claim 5wherein said semiconductors are made of bismuth telluride.
 7. Theminiature cooler of claim 5 wherein: the storage compartment furtheradditionally includes a Dewar flask, in which the articles to be storedare placed.
 8. The miniature cooler of claim 5 wherein: the volume ofthe storage compartment is less than 250 cc.
 9. The miniature cooler ofclaim 5 wherein: the power output of the solar battery is less than 10W.
 10. The miniature cooler of claim 5 and further comprising a belt forattachment of said cooler, said belt for wearing around the waist of aperson.
 11. The miniature cooler of claim 1 and further comprising abelt for attachment of said cooler, said belt for wearing around thewaist of a person.